Code transmitting apparatus in track circuit signaling systems



Q 4 .m f m 8 1 5 m m M, a i 5ml m m ww m I 5, s SA QM 2 u m 5o.... 2 .MWa. Imi@ M A SCHEG CODE TRANSMITTING APPARATUS IN TRACK CIRCUIT SIGNALINGSYSTEM July 3, 1951 July 3, 1951 Filed Aug. 51, 1944 M. A. scHEG2,559,468

CODE TRANSMITTING APPARATUS IN TRACK CIRCUIT SIGNALING SYSTEM 2Sheets-Sheet 2 :inventor (Ittorneg Patented July 3, 1951 CODETRANSMITTING APPARATUS IN TRACK CIRCUIT SIGNALING SYSTEMS Marcian A.Scheg, Rochester, N. Y., assignor to General Railway Signal Company,Rochester,

Application August 31, 1944, Serial No. 552,108

4 Claims.

The present invention relates to block signalling systems for railroadsusing coded track circuits, and more particularly pertains to theimprovement of the code transmitting apparatus employed in suchsignalling systems.

Each block of a signalling system employing coded track circuits usuallycomprises a single track circuit extending throughout the length of suchblock with suitable code transmitting apparatus at one end of the trackcircuit and suitable code responsive means at the other end. The codetransmitting apparatus usually applies code pulses at differentdistinctive rates to provide the different codes in accordance withtraic conditions, although Various different types of codes may beemployed. Since coded track circuits are thus usually relatively long,as above mentioned, a substantial current iioW occurs during theapplication of each code pulse especially when the ballast along thetrackway drops in resistance to its lowest value under adverseconditions. Also, when a train enters a block and shunts the track railsat the code receiving end of the track circuit, the code transmittingapparatus continues operation at the leaving end of the block and in sodoing must supply a relatively large current during the application ofeach code pulse.

In View of this fact that the code transmitting apparatus of a codedtrack circuit must under :y

certain conditions supply code pulses of relatively high current valuesat very low potentials, it is apparent that a problem is presented inproviding contacts on the' code transmitting apparatus which willadequately handle such relatively high currents and yet be ofsufficiently low Contact resistance as to not materially affect theapplied potential.

The present invention proposes to obviate these difficulties by applyingdirect current code pulses to the track rails of a track circuit througha rectier supplied from an alternating current source with suitablemeans for controlling the application of the alternating currentpotential to the rectier in a manner so as to minimize the value ofcurrent to be broken by the coding contacts, Since the energy is to beprovided from an. alternating current source, it is proposed that thecoding contacts control the energy at potentials higher than thatsupplied to the track r rails but with correspondingly reduced currentValues, and in this way make it possible to employ relatively highresistance non-arcing contact material, such as tungsten, or the like.

In many coded track circuits it is not only desirable to transmit drivencode pulses in one direction over the track rails, but it is also de'-sirable to transmit so-called inverse code pulses between the successivedriven code pulses in an opposite direction over the track circuit. Inorder to accomplish this, it will be evident that the direct currentcarrying circuits connecting to the track rails must be commutated inorder to include and exclude the code transmitting and code receivingapparatus at each end of the track circuit. Thus, another object of thepresent invention is to so control the application of energy through thecode transmitting apparatus as to minimize the current to be carriedbythe commutating contacts.

Generally speaking, and Without attempting to define the exact natureand scope of the present invention, it is proposed in one form of theinvention to provide the energy for a coded track circuit by connectingthe alternating current source through a full-wave rectifier with aresonated impedance included in series' with the alternating currentsource and the rectler, which resonated impedance may be shunted andunshunted by suitable code transmitting contacts so as to control thesupply of current to the track rails. In order that such coding contactsmay be of the high resistance arc: resistance type, it is proposed thatthe resonated impedance be of the auto-reactor type so as to raise thevoltage to be governed by the coding contact considerably above thatsupplied to the rectier.

It `is also proposed that the commutating contact, which is included inthe direct current: side of the rectifier so as to connect the rectifierand a code receiving relay alternately across the track rails, besuitably adjusted with respect to the coding contacts, so that thecontrol of the current by the resonated auto-reactor is effectedsubsequent to the closure of the commutating contacts and prior to theiropening.

In another form of the present invention, it is proposed that thesecondary windings of two like transformers be connected in seriesacross the terminals of a rectier but with their potenials in oppositionto each other. Under such a condition, there is no current flow throughthe rectier to the track rails. The codingk contacts are arranged tocontrol one of the transformers so as to deenergize it and remove itsopposing potential, and thus allow a potential to be applied from thedirectly connected transformer to the rectiiier to cause a current flowin the track rails. In this way, the coding contacts by controlling suchopposing transformer merely have to carry current of a sufficient valueto supply the transformer losses; While the load current is directlysupplied by the other directly connected transformer. It is alsoproposed that this form of the invention be adapted to the commutationof the low Voltage direct current portion of the connections to thetrack circuits so as to provide for the transmission and reception ofvinverse codes as Well as the driven codes.

Other objects, purposes and characteristic features ol the presentinvention will be in part obvious from the accompanying drawings, and inpart pointed out as the description progresses.

In describing the invention in detail, reference will be made to theaccompanying drawings, in which those parts having similar features andfunctions are designated by like letter reference characters which aregenerally made distinctive by reason of distinctive preceding numeralsrepresentative of their location or association with other deviceshaving reference characters with like numerals, and in which:

' Fig. 1 illustrates in a diagrammatic manner one .form' of av codedtrack circuit system embodying the present invention and employing aresonated reactor for controlling the coded track circuit energy;

Fig. 1A illustrates a modified form of inverse `code receiving trackrelay for use in Fig. 1;

Fig. 1B illustrates a modified form of resonated Vreactor for use inFig. l; and

Fig. 2 illustrates another form of coded track circuit system embodyingthe present invention in which opposing alternating current potentialsare provided to intermittently limit the current now in the trackcircuit to produce the code pulses.

For the purpose of simplifying the illustration and facilitating theexplanation, the various parts and circuits constituting the embodimentof the :invention have been shown diagrammatically and vcertain.conventional illustrations have been employed, the drawings having beenmade more with `the purpose of making it easy to understand theprinciples and mode of operation than with the idea of illustrating thespecic construction and arrangement of parts that would be employed inpractice. Thus, the various relays and their contacts are illustrated ina conventional manner, and symbols are used to indicate the connectionof terminals to batteries or other suitable sources of electric currentinstead of showing all of the Wire connections to these terminals.

` The symbols and are employed to indicate the positive and negativeterminals respectively of suitable batteries or other sources of directcurrent; and the circuits with which these symbols are employed areassumed to always have current flowing in the same direction, `althoughit is to be understood that in some cases alternating current might besubstituted for the direct current, and in such cases the and are to beconsidered as indicating the relative instantaneous polarities of thealternating current. In some of the circuits, alternating current isemployed, and the opposite terminals of a suitable source or sources forsuch alternating current circuits have been indicated by the symbols(BX) and (CX).

With reference to Fig. l of the accompanying drawings, a stretch oitrack has been divided into track sections by suitable insulated jointsof which the track section 2T has been shown completely and the tracksections iT and 3T in part only. Color light type signals and are shownat the entrance ends of the track sections 2T and 3T respectively,assuming a normal direction of trahie from left to right. These signalscan of course be of any suitable type desired.

At the exit end of each track section (such as section ZT), a suitablecode transmitting appara-n tus is located to transmit driven codes ofdiierent distinctive rates in accordance with traic conditions inadvance as governed by the code reeiving means for the entrance end ofthe next adjoining track section. This apparatus also has associatedtherewith suitable inverse or oi code receiving means which detects thepresence of an approaching train and can be used ifor approach lightingsignals, highway crossing protection, approach locking and the like.

At the entrance end of each track section (such as section 2T) asuitable code receiving apparatus is located for receiving the diiierentdriven codes and decoding them so as to properly control the associatedsignal. Also, associated with this code receiving apparatus is suitableinverse or oi code transmitting apparatus, for transmitting inverse codepulses during the ofi periods between successive driven code pulses.

As typical of all such track sections above brieiiy described, referencemay be made to the track section 2T ci Fig. l, in which a codetransmitter relay 3GP of the neutral type is energized and deenergizedin accordance with different code rates as selected by the home signalrelay 3H associated with the signal 3. More specifically, when irontcontact 5 of relay 3H is closed, a coding contact |800 energizes therelay 3GP at the clear code rate of 180 times er minute, but if the backcontact 5 of relay 3H is closed the relay 3GP is energized at thecaution code rate of 75 times per minute. v It is to be understood thatthe relay 3H is rie-energized whenever a train is in the track section3T, but is picked up when ever a caution or clear code rate is beingreceived at the signal 3 location. Also, the usual clear and cautioncode rates of '75 and 180 pulses per minute have been selected for thecoders C and I50C for the purposes of this disclosure, but it should beunderstood that other suitable code rates might be selected.

Each of the code transmitter relays, such as relay BCP, is provided withat least two contacts, one of which is conveniently termed an advancedcontact while the other oi which is termed a retarded contact. Eachadvanced contact a is so connected to its operating armature as to closeits front contacts prior to the closure of the front contact of itsassociated retarded contact b; while the opening of the advanced frontcontact a is effected subsequent to the opening of the retarded contactb. Although this relative advance and retardation of contacts a and bmay be of any suitable amount for accomplishing the purposes of thepresent invention, it has been found in one typical embodi-1 ment thatthe advanced contact a may be closed approximately ten thousandths oi aninch earlier than the retarded contact h, which inference in inches ofcourse refers to the air gap adjustment. This relative closing of thecontacts has been inu dicated on the drawing by a suitable legend.

Also, associated with the leaving` end of track section 2T is an inversecode receiving track relay SATR. This relay is or the magnetic sticktype as indicated in the drawings, and thus its contacts are operated toopposite positions upon the energization of such relay in opposite directions, and such contacts remain in their last actuated positions untilthe relay is energized in the opposite direction. This relay is shown ashaving three windings for purposes which will be described hereinafter.

The opposite terminals (BX) and (CX) of a suitable alternating sourcesupplies energy to the primary winding of a transformer STF, and thesecondary of this transformer supplies energy at a suitable voltage tothe input terminals of the rectiier 3R. The current ow in this circuitmust pass through the winding 6 of an autoreactor unit 33T which has asecond winding '1. Connected across the outer terminals of theautoreactor BRT is a suitable condenser 9 which is preferably of such avalue as to resonate the inductive reactance of the auto-reactor BRT,although it should beV understood that the inventions may be practice-:lalthough exact resonace is not accomplished. The resonant condition isoi course for the same frequency of alternating current as supplied tothe transformer STF. The outer terminals of the auto-reactor BRT areshunted and unshunted by Contact 3 of the code transmitting relay 3GP,as will presently be described.

The primary winding of the transformer STF may be connected to the usualcommercial supply of 60 cycle alternating current at 110 volts forexample, while its secondary winding may be of such a ratio as toproduce 6 volts, for example. This voltage supplied to the input of therectifier through the winding 6 of the auto-reactor SRT will supply arelatively small. current through front contact l0 of the transmitterrelay BCP to the track circuit when this advanced Contact l0 initiallycloses and connects the output of the rectiiier 3R through the resistorIl to the lower track rail and the other terminal of the rectiiier 3Rthrough the lowest winding of the inverse track relay BATR to the upperrail of the track section 2T. This is because the resonant impedance ofthe auto-reactor SRT is very high and limits the current to a low valuesuch as '75 milliamperes for example. But as soon as the retardedcontact 8 closes its front points, the outer terminals oi theauto-reactor SRT are shunted so that the impedance of the autoreactor 3Ris reduced to substantially the resistance drop through its winding 6,and the current thus supplied to the track rails of the track section 2Tis in accordance with that required under the particular adjustment ofthe limiting resistor l! and the conditions of the track sectionincluding the track relay 2TH. This is because the closure of irontcontact 8 shunts the condenser 9 and destroys the resonant condition,and also shunts the eiective secondary of the auto-reactor RBT whichreduces its inductive reactance to substantially Zero. The winding 6 ofthe auto-reactor 3RT is of relatively large wire so that its resistanceis low compared to winding 1, Thus, the eiiect of the auto-reactor SRTon the input to the rectier 3R is relatively slight under its shuntedcondition. The current which iiows in the lower winding of the inversecode receiving track relay SATR passes through the relay in such adirec'- tion as to cause its contacts to be moved to their lower ordropped away positions, as indicated by the arrow within the lowerwinding.

Since the Winding l of the auto-reactor 3RT has a greater number or"turns than the winding E, the potential across the outer terminals ofthe auto-reactor 3RT, before the outer terminals are 6. shunted, isconsiderably higher than. the' potential given by the secondary windingof the transformer aTF, and this higher potential may be made of anydesired value by properly selecting the ratio of the two reactorwindings. However, this potential should be suiciently high. that theretarded contact 3 may be constructed of suitable relatively highresistance arc resisting material, such as tungsten, for example, sothat it may readily produce a shunt across the outer terminals of thereactor and yet provide a sturdy and reliable contact for breaking anycurrent flow upon the opening of the contact 8.

It will be mentioned at this point that the advanced contact Iii ispreferably constructed of a suitable low resistance material such assilver' so that the relatively low potentials applied to the trackcircuit will not be materially changed by the inclusion of the contact,and so that such potentials will be reliably maintained at the samevalues for successive impulse periods.

At the end of each pulse period the relay 3GP is dropped away thusopening the retarded contact 8 prior to the opening of advanced contactiii. The opening of contact i3y of course unshunts the auto-reactor SRTand its inductive reactance is inserted into the input circuit of therectifier 3R. prior to the opening of contact Hl. This reduces thecurrent in the track circuit energy applying circuit to a very lowvalue, so that the opening of contact I0 breaks a relatively smallcurrent such as '.75 milliarnperes as compared to a track circuit pulsecurrent which may under some conditions be as high as l0 to l5 amperes.Any arc which is made at the contact B has a very small current value inview of the reactor Winding ratio and the relatively high resistance ofwinding l. Also, any arc that might be produced at this contact issubstantially absorbed by the confenser S. In other words, the condenser9 serves two purposes, namely, that of resonating the auto-reactor ERT,and also suppressing any arc across the contact 8.

While the back contact l0 of the transmitter relay 3GP is closed, theintermediate winding of the inverse code receiving track relay SATR isconnected across the track rails of section 2T for receiving an inversecode pulse, if there is one, and actuating its contacts to an upperposition as indicated by the arrow included within its winding. Theoperation of the driven code receiving and inverse code transmittingapparatus at the other end of the track section 2T will be describedhereinafter, but for the present it is 1 sufiicient to understand thatan inverse code pulse may be received at the leaving end of the tracksection 2T and this will flow in such a drection that the contacts ofthis relay ATR are picked up. This differential connection of thewindings of relay ATR will be readily apparent from the drawing of thecircuits. current flow in the inverse track relay SATB, during aninverse code pulse can be suitably adiusted by the limiting resistor I4.Upon the cessation of the inverse code pulse, and when the next drivencode pulse is applied by the transmitter relay SCP in a picked upposition, the current flow `through the lower winding of the relay SATRis in such a direction to cause its contacts to be actuated to theirlower positions.

lt will thus be seen that this relay SATB, is alternately operated toits opposite positions, being caused to have its contacts moved to theirupper positions by inverse code pulses and having its contacts moved tolower positions in response to driven code pulses. Upon the cessation ofinverse code pulses, the contacts of the relay are of course maintainedin their lower positions to which they are actuated by the first drivencode pulse following the last received inverse code pulse.

Associated with this inverse code receiving track relay BATR, is asuitable decoding relay SAH which has an associated decoding transformerI2 of the usual mid-tapped type controlled by contacts on the relaySATB, in the usual way. Thus, whenever the relay SATB, receives inversecode pulses, the relay .'iAH is picked up, but when the relay SATRceases to receive inverse code pulses this relay SAE-I is dropped awayto close its back contact i3 and thus approach light the signal 3.

It will be appreciated that each inverse code pulse will be ofrelatively short duration, and since the relay SATR is restored to itsdropped away position due to the application of the driven code pulse,it will be readily apparent that the relay BATH would ordinarily be in apicked up position for a relatively short time compared to the durationof an "oi period or an on period of the driven code. But in order thatthe contacts of the relay 3ATR. may be in their picked up positions forsuch a time as to make the picked up condition of substantially the sameduration as the dropped away condition during the reception of inversecode pulses, it is proposed to make the relay SATB. slow to be restoredto its lower position, although quick to be operated to its upperposition in response to a relatively short inverse code pulse. with themagnetic stick type relay BATR, its upper winding is provided with ashunt circuit through a front contact I5. The slow action produced bythe shunting of this upper winding, is eiective only upon theenergization or the relay by energy during a driven code pulse iiowingthrough a local circuit of the relay to delay its operation to its lowerposition. The amount oi retardation may be regulated by the number oiturns and resistance of such turns as shorted through this contact I5,but it is preferable that this be arranged so as to cause the relay SATRto be picked up for substantially the same time that it is dropped away.This gives a better decoding operation of the relay SAI-l.

At the entering end of the track section 2T, and associated with thesignal 2, is a track relay 2TR, which is preferably of the polarizedtype, that is, its contacts are biased to one position by gravity orsuitable resilient means, and are operated to picked up or actuatedpositions in response to only a particular polarity. This track relayZTR is connected through a limiting resistor 2D and the advanced backcontact 2l of the repeater track relay ZTPA to the track rails of thetrack section 2T. Each driven code pulse causes the contacts of therelay 2TH to be picked up, while the deenergization of the track section2T between two successive driven code pulses results in the releasing ofthe contacts of this relay 2TR. The successive operation of the trackrelay ZTR in response to driven code pulses causes suitable decodingapparatus to be controlled through contact 22 so as to pick up thedistant relay 2D in response to the clear code of the 18) code rate aswell as the home relay 2H, out to pick up only the relay 2H in responseto the caution code of the '75 code rate. Whenever no code is receivedboth of these relays 2H and 2D are deenergized This decoding apparatusmay be of To accomplish this result any suitable type such as shown forexample in the Patent No. 2,342,489 granted N. D. Preston February 22,1944, or such as shown in Fig. 2 of the accompanying drawings, but onlythe dotted rectangle has been indicated for the sake of simplicity inthe disclosure of this Fig. 1.

It will of course be understood, that suitable driven code transmittingand inverse code receiving apparatus is associated with the leavin-g endof track section IT, but this has been merely indicated by a suitabledotted rectangle in which the relay ZCP is shown and from which theinverse decoding relay 2AH is indicated as controlled. This apparatus isof course the same as that shown at the leaving end of track section 2T.Normally inverse code pulses are being received so that the relay 2AI-Iis picked up, but assuming that a train is approaching on the tracksection IT, this relay QAH would be dropped away closing its backcontact 23. Assuming that a clear code is being received by the trackrelay 2TR and the associated decoding apparatus, circuits would beclosed from (-1-) through back contact 23, front contact 24 of relay 2H,front contact 25 of relay 2D, the green lamp G of signal 2, to thuscausing signal 2 to give a clear indication. Ii, however, a caution codewere being received by the decoding apparatus, the distant relay 2Dwould be dropped away while the relay 2H would be picked up so that theyellow or caution lamp Y of signal 2 would be energized through backcontact 25. On the other hand, ir" a train were standing in the tracksection 2T, so that no code is being received by the coding apparatus atsignal 2, both the relays ID and 2H are dropped away and the red lamp Rof signal Z is energized through back contact 24 of relay 2H, thuscausing this signal 2 to indicate danger or stop.

Upon each deenergization of the track relay ZTR during the reception ofa driven code7 a circuit is closed through back contact 25 forenergizing the repeater relay ZTPB by an obvious circuit. During itspick up period, which may be suitably adjusted by well-known means anddesign of such a relay, a circuit is closed for the inverse codetransmitting relay ZTPA. from (-1-), through back contact 26 of relayZTR, back contact 2l of relay 2TPB, winding of relay ZTPA, to As soon asthe relay ZTPB picks up and opens back contact 2l, the relay ZTPA isdeenergized. The relative pick up and drop away times of these relays isso selected and organized that the relay ETPA is picked up for a shortperiod during each deenergization of the track section 2T betweensuccessive driven code pulses.

The closure of the advanced contact 2 I oi relay ZTPA connects theoutput terminals of the rectiiier unit ZRA through a limiting resistor3'! to the track rails of section 2T. Since the transformer ZTFA issupplied with alternating current from a suitable source indicated by(BX) and (CX) its secondary Winding applies a voltage through thcwinding 3| of the auto-reactor ZRTA to the input of the rectifier unitZRA. Thus, the output of the rectier ZRA supplies a potential to thetrack rails, but the current flow in this circuit is relatively smallsince the impedance of the resonated auto-reactor ZRTA is relativelyHowever, as soon as the retarded contact 255 of relay ZTPA closes, theouter terminals o1 the auto-reactor 2RTA are shunted, which reduces thereactancc to substantially zero, so that substantially the full voltageof the secondary winding of the transformer ZTFA is applied to the inputoi the rectiiier unit ZRA. Thus, an inverse code pulse is applied to thetrack section 2T of a value as determined by resistor 3l and theconditions of the track circuit, which inverse code pulse is received bythe inverse code track relay SATB., as previously described. Theauto-reactor ZETA is constructed and is controlled by the retardedcontact 28 of relay ZTPA in exactly the same way as described for theauto-reactor SRT used to control the driven code pulses. In other words,the advanced contact 2| of relay ZTPA may be constructed of suitable lowresistance material, such as silver, since only a relatively lowpotential and current is controlled by this contact, while the retardedcontact 28 may be constructed of suitable high resistance contactmaterial, such as tungsten, for reasons previously explained. Thecurrent controlled by the contact 28 is relatively low in View of thewinding ratio of the auto-reactor 2RTA, and the associated resonatingcondenser 29 acts to absorb any are at the contact 28 when it is brokenat the end of the inverse code impulse period. It can be seen from theabove that each inverse code pulse period is of a yduration equal to thepick up period of the relay 2TPB together with the drop away period ofthe relay ZTPA, and these values are so chosen, as above mentioned, thatthe inverse code pulse will cease in plenty of time before the drivencode pulse is applied at the opposite end of the track section.

Although for the purposes of this particular embodiment of the presentinvention, auto-reactors, such as SRT and 2R'IA are used for controllingthe driven code pulses, and for controlling the application of theinverse code pulses, it

should be understood that a usual transformer with separate primary andsecondary windings could be just as well employed and still accomplishthe functions of the present invention. Such an organization is shown inFig. 1B, where the primary winding of such a transformer SRTl isconnected in the input of the rectier 3R the same as winding 6 of Fig.1; while its secondary has the condenser 9 connected across its outerterminals, and such outer terminals are shunted and unshunted by thecontact 8 of the transmitter relay SCP. Since the characteristics of thesecondary load are transferred to the primary of a transformer, thecondenser 9 connected across the secondary has such a value as toresonate the transformer and also to act to absorb or suppress anyarcing from the associated controlling contact. The operation of such amodication is exactly the same as that already described. Although theauto -reactor has been disclosed as a preferred form, it is to beunderstood that any embodiment of the invention using a transformerhaving separate primary and secondary windings is intended to be withinthe scope of the present invention.

As above mentioned, the inverse code receivf ing track relays, such as3ATR for example, are preferably made slow acting in being actuated totheir lower or dropped away positions. In Fig. l. this is acomplished bythe provision of a front contact shunting the upper winding of therelay. But it is to be understood that this may be accomplished indifferent ways such as shown for example in Fig. 1A, where a rectifierunit 3@ ,is shown as shunting the upper winding of relay ZATRI. Thisrectifier 3B is included in the shunting circuit for this upper windingin such a direction that the inductive impedance of this upper windingis effective when the lower winding is energized in a direction toactuate the contacts to their lower positions, but is 'not effective(due to its high resistance to current ow in a backward direction) whenthe intermediate winding of the relay is energized by an inverse codepulse. The complete circuits have not been shown in Fig. 1A, since it isto be understood that this relay SATR1 may be directly inserted in Fig.1 in place of the relay SATR.

Fig. 2 form of the inventionitfith reference to the accompanying Fig. 2of the drawings, a stretch of track has been divided into track sectionsby suitable insulated joints of which the track secton '5T has beenshown completely and track sections 41T and ET in part only. Color lighttype signals 5 and 6 are shown at the entrance ends of track sections 5Tand 6T respectively. These signals can of course be of any suitabledesired type.

At the exit end of each track section is suitable driven codetransmitting apparatus governed by the code receiving apparatus for theentrance end of the next adjacent track section in advance, so as toapply different driven codes. in accordance with traffic conditions inadvance. At the entering end of each track section is r suitable codereceiving organization indicated in the drawings as including a trackrelay ETR of the polarized biased type, this is, this relay ERT respondsto only a particular polarity to be actuated to an operating position,and is biased to a normal position.

Each code following track relay, such as relay ETR, governs suitabledecoding apparatus of any well-known construction, such as shown forexample in the Patent No. 2,342,489 granted to N. D. Preston February22, 1944, and such decoding apparatus has been diagrammaticallyillustrated as including a decoding transformer di] which has amid-tapped primary winding controlled by contact 4i of the track relaySTR so that this transformer is energized in opposite directionsalternately as the Contact il of the track relay ETR is operated to itsopposite positions in response to driven code pulses. lThe secondarywinding of this decoding transformer 43 is midtapped and connected tothe home relay 5H in combination with a rectifying contact i2 so thatthe relay 5H is picked up whenever the track relay ETR is receivingdriven code pulses of either the clear or caution code rates, but isdropped away whenever there is an absence of such code pulses. Asuitable tuned decoding transformer 38 has its primary connected toanother secondary winding of the transformer 4D, while its secondary isconnected through the rectifier Aunit 113 to the distance relay D. Thiscircuit is tuned by the condenser 3S so as to pick up the relay 5D onlywhen the track relay 5TR is operating at the clear code rate which forthe purposes of this disclosure is to be pulses per minute.

These home and distant relays 5H and 5D govern the indications of theassociated signal 5, as will vbe readily understood from the drawings,while the home relay 5H also acts to select between the particularcoding contacts which are to govern the driven code rate for thetransmitting relay for the section next in the rear (not shown). Suchcoding contacts SSC and 75C have been shown as associated with thesignal 6, and these contacts are assumed to be operating 180 times perminute and '75 times per minute respectively to provide the usual coderates, but it will be readily appreciated that various other rates maybe selected if desired. These coding contacts 180C and 75C may be of any11 suitable type, that is, they may be motor driven, or they may be codeoscillators of the type dis closed in the patent to O. S. Field No.2,351,532?. dated June 20, 1944.

At the exit end of each track section, such as shown for the tracksection T, a transformn er ETFA has its primary winding energized fromthe opposite terminals (BX) and (CX) of a suit able alternating currentsupply; while its secondary Winding is connected in series with thesecondary winding of a like transformer STIPB across the oppositeterminals of the input of e. full-wave rectifier 5R. The output of therectifier GR is connected through the limiting resistor 44 to the railsof the track section 5T.

The primary winding of the transformer STF@ is supplied with alternatingcurrent from the same source as transformer G'IFA when the back contact45 of relay GCP is closed. Since the primary-secondary Winding ratios ofthe trans-- formers ETFA and G'IFB are substantially iden-- tical, andsince the windings of the transformers are so connected that the outputpotentials of their secondaries are in opposition, there is no potentialapplied to the rectifier 5R under such condition. On the other hand,when the conu tact 45 of the relay BCP is picked up, the alternatingcurrent energy is removed from the primary winding of the transformer'IFB, and such primary winding is also shunted through front contact 45.This not only removes the opposing potential of the secondary windingfrom the series circuit across the rectifier, but also substantiallyremoves the inductive reactance of such transformer so that a potential,as supplied by the secondary winding of the transformer G'IFA, isapplied to the opposite terminals of the rectier 6R. The output of therectifier 5R is fed to the rails of the track section to energize relay5'IR at the entering end. It is noted here that the track relay 5TH, atthe entering end is connected across the track rails through limitingresistor 46 and back contact 4T of relay 5TPC.

The condenser 48 and a series resistor 49 are connected across theopposite terminals of the secondary of transformer GTFB and in multiplewith front contact 45 of relay SCP so as to act as an arc suppressingunit for the front contact 45. It should be noted that condenser 48 doesnot resonate transformer WIFE, nor does it materialf 1y affect the phaseof the output of the secondary of transformer GTFB because of the lowcapacity of such condenser.

The code transmitting relay SCP is controlled through front and backpoints 50 of relay 6H so as to be operated at the selected code rate,and while front contact 45 of relay GCP is closed, code pulse energy issupplied to the track section 5T, :but when back contact 45 is closed,the opposing potential of the secondary of transformer STFB prevents theflow of current to the track rails of section 5T. In this way, codepulses are applied to the rails of the track section 5T at theparticular selected code rate.

Each track section has associated therewith an inverse code receivingrelay ATR at the leaving end and suitable inverse code transmittingapparatus at the entering end of the track section including a rectifierSRA, a transformer ETFA and a transformer `ETFB, as well as atransmitting relay 5TPC controlled through repeater relays 5TPA and 5TPBas will presently be described.

Since it is desired to first point out the operation of the driven codetransmitting apparatus,

it will be assumed for the present that only a driven code is beingtransmitted through the track section. It will be apparent that thecurrent supplied through back contact 45 to the transformer G'IFB ismerely of a suicient amount to supply the power losses of suchtransformer, and that the closure of front contact 45 causes a currentflow through it, although the actual current of the driven code pulse issupplied by transformer ISTFA. The front contact 45 and circuit shuntingthe primary of transformer TFB will carry a current having a Valuedependent upon the potential drop across the secondary of thetransformer GTFB and dependent upon the ratio of turns between theprimary and secondary windings. Since this is a short circuit conditionfor thetransfcrmer E'IFB, the potential across the secondary winding ofthis transformer will be fairly low because of the impedance of thetrack circuit load, so that the current through front contact 45 is notexcessive. But since there will be some magnetic uX change in thetransformer due to the opening of front contact 45 at the end of theimpulse period, it is desirable to employ the condenser 48 and theseries resistor 49 connected in multiple therewith to absorb any suddenchanges in current conditions produced by the opening of front contact45. In other words, although the arrangement of the transformersprovides for a minimum of arcing at the contact 45, it is desirable tofurther reduce this arcing by the use of condenser 48. The seriesresistor 49 is included so that should the condenser 48 be substantiallycharged during the change-over of the contact 45 from a back point to afront point, the discharged current of the condenser will be limited bythe series resistor 49.

The voltage supplied to the primary winding of the transformer GTFB maybe of any suitable Value, such as a commercial volt supply, but sincethis value is usually a relatively high potential, as compared to thetrack circuit potentials Which may be in the order of S volts, forexample, the contact 45 can be readily constructed of a relatively highresistance material, such as tungsten, and thus provide for long andreliable service. In other words, higher contact resistance materialsmay be used in such a circuit, since the potential is suflicient tobreak down any contact resistance and thus reliably supply the requiredcurrent.

Assuming that each track section of a block signalling system isorganized as above described, and that a clear code is being receivedover the track section 6T so that the home relay `(SH is picked up, thenthe relay GCP is being operated at the 180 code rate, and the signal 5is of course indicating green or proceed. On the other hand, if therelay 6H were deenergized due to the absence of code in the tracksection 5T, the relay SCP would be operated at the 75 code rate anddriven code pulses would be applied to the track section 5T in a mannerabove described. These impulses would be received by the track relay5'IR causing the signal 5 to be controlled in accordance with suchcodes.

When a 180 code is received at the signal 5, the track relay 5'IRoperates contact 4| at the 180 code rate so that should a train approachthis signal and cause the deenergization of the approach decoding relay5AII and close back contact 5l, then the signal 5 would indicate greenby reason of a circuit from (-1-) closed through back contact 5l ofrelay 5AI-I, front contact 52 of relay H, front contact 53 of relay 5D,lamp of signal 5, to But if a 75 code is being received, then the relay5D will be dropped away and the yellow lamp Y will be energized throughback contact 53. On the other hand, if there is no code being receivedat signal 5 due to the presence of a train in track section 5T, bothrelay 5D and 5H will be dropped away, so that the red lamp will beenergized through back contact 52 of relay 5H.

The transmission and reception of inverse code pulses will now beconsidered. More speciiically, upon the reception of each driven codepulse, the relay 5TR is picked up closing front cotnact 4l which causesvcurrent to flow through the upper half of the primary winding of thetransformer 30. When this contact 4l assumes its lower or dropped awaypoistion upon the end of the driven code pulse, then the inductivereactance of the transformer 4B causes a surge of energy to charge thecondenser 54 and in so doing causes a current fiow through the upperwinding of the relay 5TPC of sufficient value and in a direction properto pick up its contacts. Since the relay ETPC is of the magnetic sticktype, its contacts remain in picked up positions after the surge ofcurrent through its upper windings has ceased.

At substantially the same time, the closure of back contact @l causescurrent to flow through rectifier unit 55 and through the relays 5TPAand 5'I`PB in multiple, the circuit for relay 5'IPB including backcontact 5S of relay 5TPA. The relay BTPB picks up after a short intervalof time followed by the picking up of the relay BTPA which opens thecircuit for relay 5'I'PB at back contact 56. In other words, the relaySTPA is slightly slower to pick up than the relay 5TPB, and this can beaccomplished by adding a suitable resistor in multiple with the relay5TPA.

After a short interval of time, the relay STPB releases, and thisinterval of time can be made of suitable value by adding a rectifierunit in multiple with its windings, and thus slightly delay its dropaway. But when the relay 5TPB drops away, the relay STPA is still pickedup, so that there is a circuit from (-l) through front contact 5l ofrelay S'IPA, back contact 58 of relay 5TPB, front contact 59 of relay5TPC, lower winding of relay ETPC, to The current which iiows in thiscircuit is of such a direction as to cause the contacts of the magneticstick type relay BIPC to be actuated to their lower positions to opencontact 59 and immediately break such circuit. This happens before theend of the off period between two successive driven code pulses. Inorder to suppress any arcing which may occur at contact 59, a suitablecondenser B may be placed in multiple with the lower winding or relayETPC.

Thus, it can be seen that at the end of each driven code pulse, therelay STPC is actuated to a picked up position to apply an inverse codepulse to the track section 5T, and after a short period of time isrestored to mark the end of the inverse code pulse.

More specifically, when the relay 5'IPC is picked up it opens backcontact 4T to disconnect the track relay STR, and closes front lcontact4l to connect the output of the rectifier unit 5RA through the limitingresistor S2 across the rails of the track section 5T. rlhe opening ofback contact 53 of relay 5TPB disconnects the source of energy from theprimary of the transformer S'IFB, and shunts such winding through frontcontact 53 to remove the inductive reactance of this transformer fromthe input circuit of the rectifier 5RA so that it can receive thenecessary energy from the secondary of transformer 5'IFA. The backcontact 63 of relay 5TPB is opened and its front contact is closedvslightly after the front contact 4l of relay 5TPC is closed. On theother hand, the relay 5TPB must drop to close its back contact 58 beforethe relay 5TPC is actuated to its lower position, thus, the back contactt3 is closed applying a potential in opposition to the potentialproduced by the secondary winding of transformer 5TFA before the frontcontact 4i is opened and the back contact 47 closed. In this way, thecontact lll is used to commutate the track relay and inverse code energyapplying circuit across the track rails at times at Iwhich there is noenergy iiow to the track trails. For this reason, there is no arcing atthe front and back points of the contact 47, and these contacts may beof suitable low resistance contact material, such as silver for example.The energy controlling contact 63 may be. constructed of suitable highresistance contact material, such as tungsten, since it controls thelosses in the transformer 5TFB at a relatively high voltage, asdescribed in connection lwith contact "l5 of the relay SCP.

he application of an inverse code pulse to the track section 5T occursat a time when the driven code transmitting relay GCP is dropped away,so that there is no potential across the input terminals of therectifier 6R. The inverse code energy iiows from the lower track railthrough the rectifier unit GR and the limiting resistor 411 to the uppertrack rail. This produces a potential drop across the rectifier and thelimiting resistor All so that a current flow is produced in the lowerwinding of the relay EATR to the right and through back contact 64 ofthe transmitting relay BCP to the upper terminal of resistor 41S. rThiscauses the contacts of the inverse code receiving track relay SATR to hepicked up, and since this is a magnetic stick type relay. its contactsremain picked up although the inverse code pulse ceases. It should benoted in this connection, that the potential across the lower winding ofrelay GATR is during an inverse code pulse substantially the same asthat across the track rails, except perhaps for the potential drop thatis caused in the lead wires from the track. Although the rectifier unitSR and limiting resistor lili are shunted across the track rails ofsection 5T under such a condition, it should be recognized that such ashunt has a higher effective resistance than would at first be apparent,because the relatively low potential at this end of the track circuitiinds that the forward resistance of the rectiner unit 6R is relativelyhigh, which forward resistance is added to the particular adjustment ofthe limiting resistor 44. In other Words, rectifier units, especiallythose of the copper oxide type and the like, have a relatively highforward resistance for low potential and current values. The rectifierunits when employed for applying energy te the track circuit are dealingwith higher potentials and the forward resistance is relatively low, butwhen used to receive energy over the track rails at very low potential,the resistance is higher accordingly, and this factor should be takeninto consideration in considering the potential drop across the low;rwinding of the relay SATR upon the reception of inverse code pulses.

Upon the following driven code pulse, the rela-y tCP is picked upclosing front contact 64 so that the lower winding of relay A'IR isconnected through limiting resistor 55 to the output terminals of therectifier unit 5R, causing cui rent to now in a left-hand directionthrough the lower winding of relayT SA'IR actuating its contacts totheir lower or dropped away positions. In this way, the relay SATR ispicked up upon each inverse code pulse and is caused to be dropped awayupon each driven code pulse by reason of a local circuit. The actuationof the contacts of relay @ATR to their lower positions is caused to beretarded by reason of its upper winding being shunted by front contact99. This is so that the contacts of the relay tATR will be in theirupper and lower positions substantially the same length of time even ifthe inverse code pulses are of relatively short duration.

It will be readily apparent how a stretch of track having its severaltrack sections equipped with coded track circuit apparatus as disclosedherein will provide for the control of the signals to give threeindication signalling for the passage of tra-flic in an east bounddirection, so that a detailed consideration of the passage of a trainwill not be given, and especially since it is believed that the abovedescription clearly points out the condition of the signals during thepresence and absence of a train and the dif ferent code rates.

Having described two forms of a coded track circuit block signallingsystem employing code transmitting apparatus organized to give a minimumamount of arcing at the code transmitting contacts as embodying thepresent invention, it is desired to be understood that the invention isshown in this connection for the purpose of facilitating its disclosure,and that it can be applied to systems of various other types. Althoughthe invention has been shown embodied in two diiferent forms, it to beunderstood that other specinc embodiments and modi-- iications of theinvention may be made, and that various adaptations and alterations maybe re- ,i

quired to meet the problems of practice without in any manner departingfrom the spirit or scope of the present invention except as limited bythe appended claims.

What I claim is:

l. In a coded track circuit signalling system for a section of railwaytrack, a code transmitter comprising, a source of alternating current, arectier unit, an inductive reactor unit including windings, circuitmeans connecting said alternating current source across the rails ofsaid section through a portion of said reactor windings and rectifierunits in series, and a coding contact intermittently acting to shuntsaid reactor windings to thereby permit the intermittent application ofdirect current code pulses to said section of track.

2. In a coded track circuit for railroads, a driven code transmittercomprising, a code transmitter relay having a contact intermittentlyoperated to its opposite positions in accordance with different selectedcode rates, a full-wave rectifier unit having input and outputterminals, circuit means effective to connect the output terminals ofsaid rectifier across the rails of said track section, a reactor unit ofthe auto-transformer type having a condenser connected across its outerterminals to effect .its resonance at a particular frequency, and havinga mid tap connected to one input terminal of said rectifier. a source ofalternating current connected to the other input terminal of saidrectifier and one outer terminal of said auto-transformer, and circuitmeans including said contact of said transmitter relay forintermittently shunting the outer terminals of said auto-transformer,whereby a succession of driven code impulses are applied to said trackrails which impulses are controlled by said contact of said transmitterrelay at a potential substantially higher than the actual potentialapplied to said track rails.

3. In a code transmitting organization having driven code pulsestransmitted at different code rates, a code transmitting relayintermittently operated to its opposite positions in accordance withdiiferent selected code rates and having advanced and retarded contactsboth being closed in theJ same position, but said advanced contact beingclosed slightly prior to the closure of said retarded contact and beingopened slightly subsequent to the opening of said retarded Contact, afull-wave rectifier having input and output terminals, circuit meansincluding said advanced contact for intermittently connecting saidrectifier output terminals to a track circuit, a reactor unit, a sourceof alternating current connected to the input terminals of saidrectifier through a portion of said reactor unit, and circuit meansincluding said retarded contact for shunting said reactor unit duringeach period when said rectier output terminals are connected to thetrack circuit.

4. In a coded track circuit for railroads operable to transmit oiI-codecurrent pulses in one direction during off intervals between driven codepulses transmitted in the opposite direction, code transmitting andreceiving apparatus at the driven code transmitting end of the tracksection comprising, an off-code track relay responsive to off-codepulses, a full-wave rectier having input and output terminals, atransmitter relay intermittently energized and deenergiaed in accordancewith diiferent driven code rates and including advanced and retardedcontact means, circuit means including said advanced contact meansoperated by said transmitter relay for alternately connecting anddisconnecting said 0ff code track relay and the output terminals of saidrectier across the rails of said track circuit, and circuit meansincluding an alternating current source and said retarded contact meanson said transmitter relay for applying energy to the input terminals ofsaid rectifier subsequent to each of its connections to said trackrails, said circuit means being effective to remove energy from theinput of said rectier prior to each of its disconnections from the trackrails, whereby said advanced contact means is not required to make orbreak the load current supplied to said track rails during each drivenpulse application.

MARCIAN A. SCHEG.

REFERENCES CITED The following references are of record in the file ofthis patent:

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